1. Field of Invention
The present invention relates to a magnetic element and, in particular, to a filter that is capable of eliminating the common-mode noise.
2. Related Art
The applications of the present electronic circuits have been widely spread. These kinds of electronic circuits are usually operated at high frequency, which can easily generate the electro magnetic interference (EMI). The high frequency noise can be transmitted by electromagnetic radiation or power line conduction so as to interfere the normal operation of other electronic apparatuses. The conduction EMI can be divided, according to the noise current paths, to the differential-mode (DM) noise and the common-mode (CM) noise.
In order to efficiently eliminate the EMI, the filter, which is corresponding to the type of the noise to be eliminated, is usually configured in the electronic device. For example, to eliminate the CM noise, the electronic device can be configured with a filter for eliminating the CM noise. The filter can be formed by stacking a plurality of metal coil layers and independent insulating layers. However, the properties of the filter, such as the bandwidth or the inductance value, are closely related to the layout design of the metal coil layers. The bandwidth or inductance value of the conventional filter is restricted due to the space limitation.